Interstitial oxygen induced Fermi level pinning in the Al2O 3-based high-k MISFET with heavy-doped n-type poly-Si gates

Abstract

We study the origin of substantial threshold voltage (Vth) shifts observed in Al2O3-based MISFETs with n+poly-Si gate, by focusing on the effect of an interstitial oxygen (Oi) formation in Al2O3. We observed that the Oi level in Al2O3 is 1 eV above the valence band top of Al2O3 by first-principles calculation. Therefore, O i formation and subsequent electron transfer from Fermi level to the Oi level allows the system to overcome the energy loss by the O i formation, which depends on the position of Fermi level. In case of n+poly-Si gate, this electron transfer across the interface occurs and results in substantial Vth shifts. The proposed mechanism reproduces experimental result and provides a good understanding of nano-interfacial interactions. © 2013 © 2013 Author(s).